Washing and neutralization process for synthetic fibers

ABSTRACT

ACRYLIC FIBERS HAVING GOOD WHITENESS AND BEING NON-CORROSIVE TO TEXTILE MACHINERY ARE PRODUCED BY EXTRUDING A SOLUTION OF THE ACRYLIC POLYMER IN AN ORGANIC SOLVENT CONTAINING STABILIZING ACIDS, THEN NEUTRALIZING THE ACID IN THE RESULTING FIBER WHILE WASHING RESIDUAL SOLVENT FROM THE FIBER.

A. H. BRUNER HAL Jan. 26, 1971 L WAS,HING AND NEUTRALIZATION PROCESS FOR SYNTHETIC FIBERS Filed 001:. so. 1967 COAGULATED PROCESS FIBER RoM SPIN BA TH WATER PRIMARY NEUTRALIZING ZONE D. I. WATER NEUTRAL IZER SOLUTION FINAL WASHING ZONE FIRST WASHING ZONE 7 FIG. I.

TO DRYING COAGULATEO FIBER FROM SPIN BATH D. I. WATER H NEUTRALIZER BATH I 1 SOLUTION TO WATER PROCESS RE :ovERY WATER FIG, 2.

INVENTORS ALBERT H. BRUNER THOMAS B. TRUSCOTT ATTORNEY United States Patent O US. Cl. 264-233 6 Claims ABSTRACT OF THE DISCLOSURE Acrylic fibers having good whiteness and being non-corrosive to textile machinery are produced by extruding a solution of the acrylic polymer in an organic solvent containing stabilizing acids, then neutralizing the acid in the resulting fiber while Washing residual solvent from the fiber.

BACKGROUND OF THE INVENTION This invention relates to the production of synthetic fibers, and more specifically to the productoin of acrylic fibers from acrylonitrile homopolymers and copolymers and to a novel method for washing the fibers and neutralizing any acids present in the fibers.

Wet spinning of acrylonitrile polymers from organic solvent solutions is an accepted method of producing acrylic fibers on a commercial scale. The method briefly entails dissolving the acrylonitrile polymer in a suitable organic solvent to produce a spinning solution, extruding the spinning solution through a multiorifice spinning jet into an aqueous bath to form a plurality of coagulated filaments, washing the filaments to remove residual solvent, and finally drying the washed filaments to remove moisture and produce the textile product.

When washing the coagulated filaments, it is necessary to remove certain acidic compounds as well as residual solvent in order to assure that the fiber product is not corrosive to textile machinery. The acid compounds may originate as impurities in the organic solvent, such as traces of acetic acid in dimethylacetamide solvent or formic acid in dimethylformamide solvent, or the acid may be deliberately added to the spinning solution as heat stabilizers to prevent discoloration during the preparation of the spinning solutions. Typical compounds of this nature are oxalic acid and phosphoric acid.

Neutralization of these acid compounds has been the subject of many past investigations. One method described in US. Pat. No. 3,318,983, proposes the addition of ammonium hydroxide to the wash water. Although this technique produce fair results, additional improvement was sought whereby non-corrosive fibers of still better whiteness might be produced.

SUMMARY OF THE INVENTION It has been found that substantially improved results are obtained when wet spun acrylonitrile fibers containing residual solvent and acid compounds are sequentially washed with a first wash water supply, a neutralizer water supply, and final wash water supply, effectively removing substantially all the residual solvent and neutralizing any acid compounds not washed from the fiber. The first wash water supply may be pure or deionized water, or may more economically be recovered process water containing process impurities. The neutralizer water supply is preferably deionized water containing a basic compound. The final wash water supply is necessarily deionzed water in order to reduce fiber contaminants to the lowest possible level. This method of sequential washing-neutralizationwashing produces a fiber which is essentially free of acid 3,558,765 Patented Jan. 26, 1971 contaminants and has an improved original whiteness and heat stability as compared to the fibers produced according to the methods of the prior art. Further, with the use of recovered process water in the first step, substantial cost reduction in he process is effected.

It is therefore an object of this invention to provide a method for sequentially washing and neutralizing wet spun acrylic fibers.

It is a further object of this invention to provide a method for producing non-corrosive acrylic fibers having good original whiteness and heat stability.

These and other objects of this invention will become apparent from the ensuing detailed description of the invention.

The operation of the invention is described by reference to the accompanying drawing which shows preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevation view of one preferred embodimerit.

FIG. 2 is a longitudinal section view of a second preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a cascade type washing apparatus 10 wherein the three sequential washing steps take place in a single washing trough. The coagulated fiber containing residual solvent and acidic compounds proceeds from the spin bath and enters the cascade washer at the lowest end. The process water or first Wash water supply enters the cascade through pipe 11 approximately at the midpoint of the cascade. The deionized water of final wash water supply enters at the top end of the cascade through pipe 13. The neutralizer water enters through pipe 12 located approximately midway between pipes 11 and 13 or about three quarters of the way up the cascade trough. The location of the water entry pipes defines three sequential washing zones described as the First Washing Zone, the Primary Neutralizing Zone, and the Final Washing Zone.

FIG. 2 illustrates an alternative washing procedure using wash rolls and three separate baths to provide the three cascade washing zones of FIG. 1. Countercurrent washing and conservation of water is achieved by allowing Baths 2 and 3 to overflow to the preceeding bath, while the overflow from Bath 1 is returned to water recovery or sewered to waste.

In the practice of this invention, the coagulated acrylonitrile filaments issuing from the spin bath and containing residual solvent and acidic compounds are passed through a first washing zone where a great part of the solvent is removed from the fiber. The wash water in this first zone is comprised of the overflow water from the subsequent neutralization and final washing zones, plus additional process water to swell the wash water volume during this initial washing stage. The process water may contain low levels of impurities such as solvent and acid since only partial washing of the fiber is required in this first zone.

From the first washing zone, the fiber proceeds into the neutralization zone where the acid in the fiber is neutralized by the addition of a suitable base. An excess of neutralizer may be used since any unrecated base flows down into the first washing zone and on to the wash water discharge.

The neutralized fiber passes into the final washing zone where it is extracted with deionized water to remove any residual solvent yet remaining in the fiber as well as any salts resulting from the neturalization of the acid in the preceding section. It is desirable that the fiber be washed as completely free of solvent, acids, and salts as possible in this final washing zone in order to assure the final fiber product of having maximum whiteness and heat stability.

After washing, the fiber is dried and may then be processed into textile yarns and fabrics according to established procedures.

The terms acrylic and acrylonitrile, as used herein without further description denote polyacrylonitrile. This invention is applicable not only to polyacrylonitrile, but also to compolymers, interpolymers, and blends thereof, particularly those containing at least 80 percent by weight of polymerized or copolymerized acrylonitrile. For exxample, the polymer may be a copolymer of from 80 to 98 percent of acrylonitrile and from 2 to 20 percent of another copolymerizable mono-olefinic monomer. Suitable copolymerizable mono-olefinic monomers include acrylic, alpha-chloroacrylic and methacrylic acids, the acrylates, such as methyl methacrylate, ethyl methacrylate, butyl methacrylte, methoxymethyl methacrylate, beta-chloroethyl methacrylate, and the corresponding esters of acrylic and alpha-chloroacrylic acids; vinyl chloride, vinyl fluoride, vinyl bromine, vinylidene chloride, l-chloro-l-bromoethylene; methacrylonitrile; acrylamide and methacrylamide: alpha-chloroacrylamide, or rnonoalkyl substitution products thereof; methyl vinyl ketone; vinyl carboxylates, such as vinyl acetate, vinyl chloroacetate, vinyl propionate, and vinyl stearate; N-vinylimides, such as N- vinylphthalimide and N vinylsuccinimide; methylene malonic ester; itaconic acid and itaconic ester; N-vinyl carbazole; vinyl furan; alkyl vinyl esters; vinyl sulfonic acid; ethylene alpha, beta-dicarboxylic acids, or their anhydrides or derivatives, such as diethylcitraconate, diethylmesaconate; styrene; vinyl naphthalene; vinyl substituted tertiary heterocyclic amines such as the vinylpyridines and alkyl-substituted vinylpyridines for example, 2-vinylpyridine, 4-vinylpyridine, 2-methyl-5-vinylpyridine, and the like; l-vinyl-imidazole and alkyl substituted l-vinylimidazoles, such as 2-, 4-, or S-methyl-l-vinylirnidazole, vinyl pyrrolidone, vinylpiperidone, and other mono-olefinic copolymerizable monomeric materials.

The polymer can be a ternary interpolymer, for example, products obtained by the interpolymerization of acrylonitrile and two or more of any of the monomers, other than acrylonitrile, enumerated above. More specifically, and preferably, the ternary polymers contain from 80 to 98 percent of acrylonitrile, from 1 to percent of a vinylpyridine or a l-vinylimidazole, and from 1 to 18 percent of another copolymerizable mono-olefinic substance, such as methacrylonitrile, vinyl acetate, methyl methacrylate, vinyl chloride, vinylidene chloride and the like.

The polymer can also be a blend of polyacrylonitrile or a copolymer of from 80 to 99 percent acrylonitrile and from 1 to 20 percent of at least one other monoolefinic copolymerizable monomeric substance with from 2 to 50 percent of the weight of the blend of a copolymer of from 30 to 90 percent of a vinyl substituted tertiary heterocyclic amine and from 10 to 70 percent of at least one other mono-olefinic copolymerizable monomer. Preferably, when the polymeric material comprises a blend, it will be a blend of from 80 to 99 percent of a copolymer of 80 to 98 percent acrylonitrile and from 2 to 20 percent of another mono-olefinic monomer, such as vinyl acetate, with from 1 to 20 percent of a copolymer of from 30 to 90 percent of a vinyl-substituted tertiary heterocyclic amine, such as vinylpyridine, a l-vinylimidazole or a vinyl lactam, and from 10 to 70 percent of acrylonitrile to give a blend having an overall vinyl-substituted tertiary heterocyclic amine content of from 2 to 10 percent, based on the weight of the blend.

While the preferred polymers employed in the instant invention are those containing at least 80 percent acrylonitrile, generally recognized as the fiber-forming acrylonitrile polymers, it will be understood that the invention is likewise applicable to polymers, copolymers, interpolymers and blends containing less than percent of acrylonitrile and as low as 35 percent acrylonitrile. Polymers containing from about 35 to 80 percent acrylonitrile may be copolymerized, interpolymerized and blended with any of the mono-olefinic monomers enumerated herein. For example, the process is applicable to fibers formed from a copolymer of approximately 40 percent acrylonitrile and 60 percent vinyl chloride and to a polymer of approximately 67 percent acrylonitrile, 21 percent vinyl chloride and 12 percent vinylidene chloride.

The invention is further applicable to other vinyl polymers containing a majority of vinyl chloride, vinylidene chloride, styrene and other well known vinyl polymers and to copolymers, interpolymers and blends thereof with the mono-olefinic monomers enumerated herein. For example, fibers which are formed from copolymers of vinyl chloride and vinyidene chloride, copolymers of vinyl chloride and vinyl acetate and copolymers of vinyl chloride and vinyl formate may be treated according to the procedure of this invention.

The process water used in the first washing zone is wash water which has had the solvent removed for reuse in the spinning process. The solvent is recovered from the wash waters in as pure a form as possible so that salts, acids, and other contaminants remain in the process water. Generally, part of this water is discarded to prevent undue impurity buildup while the remainder is recycled to the washing equipment.

The neutralizer is preferably a salt of a strong base with a weak acid such as sodium bicarbonate, sodium tetraborate, disodium phosphate, trisodium phosphate, or any other basic compound which may be used as a fiber treating agent without adverse affect on the fiber. The neutralizer is preferably dissolved in water and metered into the washing apparatus at a rate sufiicient to reduce the fiber acid level to an acceptable level. The actual amount of neutralizer naturally depends upon the amount of acid present to be neutralized. For control purposes, the acid level in the final dry fiber product should be less than 0.05 percent by weight, and preferably less than 0.03 percent. At these levels, the fiber has been found to be non-corrosive to mild steel textile processing equipment.

The acid compounds present in the fiber include acid contaminants in the solvent, such as acetic acid in dimethylacetamide, or formic acid in dimethylformamide. Acids such as oxalic or phosphoric may be incorporated in the acrylic spinning solution to prevent color degradation prior to spinning. For example favorable results have been obtained by incorporating from 0.15 to 0.3 percent oxalic acid based on the polymer weight.

The following examples will serve to more fully illustrate the practice and advantages of the instant invention. The examples are intended to be illustrative only and the invention is not to be limited thereby. All parts, proportions, and percentages expressed in the examples are by weight unless otherwise indicated.

EXAMPLE I A spinning solution was prepared by dissolving 22 parts of a polymer containing 93 percent acrylonitrile and 7 percent vinyl acetate in 78 parts of dimethylacetamide solvent which contained 2 percent acetic acid. The spinning solution was extruded through a multiorifice spinnerette and coagulated in an aqueous spinbath containing 55 percent dimethylacetamide solvent. The coagulated fibers were washed substantially free of solvent and neutralized with sodium bicarbonate in a cascade washing apparatus wherein a final wash with deionized water was provided to remove residual salts, solvent, and acids from the fiber.

After drying, the fiber was analyzed for acid and measured for original color and heat stability, Original color was determined by measuring the brightness and purity of carded fiber on the GE. spectrophotometer without neutralization and with three levels of neutralizer addition.

Neutralizer Na; HPO-l, Original color percent Acid, o.w.f. percent Brightness Purity 0. 05 0. 006 89 l. l 0. 10 0.011 89 0. 9 0. l5 0. 006 89 1. 7 0. 25 0. 002 89 3. 2

Neutralizer 1 Original color Heated color NBHCOs, Acid, percent o.w.f. percent Brightness Purity Brightness Purity None 0. 165 91 2. 6 0. 30 0. 021 87 2. 7 0. 60 0. 015 90 3. 3 0. 90 0. 010 90 3. 6

Weight of NBHCOa based on weight of fiber (o.w.f.) product. 2 Calculated as acetic acid in final fiber product.

The fiber production rate for the above experiments was 22 lbs/hour. The data shows that the acid level in the fiber can be reduced to a noncorrosive level without seriously affecting the fiber color. In fact, the heated color of the neutralized fiber was slightly improved over that of the unneutralized fiber. In evaluating the fiber color, the higher brightness values: and the lower purity values indicate increasing fiber whiteness.

EXAMPLE II A spinning solution was prepared by dissolving 22 parts of a polymer containing 93 percent acrylonitrile and 7 percent vinyl acetate in 78 parts dimethylacetamide solvent to which had previously been added 0.066 part of oxalic acid so that the concentration of oxalic acid in the final spinning solution was 0.30 percent on weight of polymer. The spinning solution was extruded through a multiorifice jet into an aqueous coagulating bath containing 55% solvent at 50 C. The resulting fibers were passed into a three stage cascade washing apparatus as shown in FIG. 1 of the drawing where they were washed substantially free of solvent and neutralized with disodium phosphate. The neutralization,wasaccomplished by adding the disodium phosphate at four different levels to determine the effect of such variation on final fiber color and acid content. The results of the study are presented below:

Neutralizer 1 N am HP04, Original color percent Acid,

o.w.i. percent Brightness Purity l O.w.i.=an1ount of neutralizer based on weight of fiber. 2 Calculated as acetic acid.

EXAMPLE III The process of Example II was repeated except the amount of oxalic acid added to the spinning system was reduced to 0.15% of the polymer weight. Acid levels and fiber color for samples produced under various levels of neutralization were as follows:

In this example, where the lower level of oxalic acid was added to the spinning solution, neutralization with 0.05% disodium phosphate produced consistently noncorrosive fiber.

We claim:

1. In a'process for a preparation of fibers from acrylonitrile polymers wherein the polymer is dissolved in a solvent therefor which may contain an acid contaminant the resulting homogeneous solution is extruded into a coagulating medium which may contain an acid contaminant to produce fibers, and said fibers are subsequently washed, the improvement of washing said fibers comprising sequentially the steps of bathing the fibers first in a primary wash bath of water, second in a neutralization bath of a-basic solution of a material selected from the group consisting of sodium bicarbonate, sodium tetraborate, disodium phosphate, and trisodium phosphate, and third in afinal wash bath of deionized water.

2. The process improvement of claim 1 wherein said washing of said fibers is conducted in a continuously flowing trough, the flow direction being toward the point of entry into the trough of the fiber.

3. The process improvement of claim 1 wherein said washing of said fibers is conducted in each of three separate bathing containers, the overflow of the third of which flows into the second, and the overflow of the second of which flows into the first.

4. In a process for the preparation of fibers from acrylonitrile polymers wherein the polymer is dissolved in a solvent therefor which may contain an acid contaminant, the resulting homogeneous solution is extruded into a coagulating medium which may contain an acid contaminant to produce fibers, and said fibers are subsequently washed, the improvement of washing said fibers comprising sequentially the steps of bathing the fibers first in a'primary wash bath comprising initially introduced wash water, the overflow from a subsequent neutralization bath, and the overflow from a final wash bath; second, in said neutralizing bath comprising an initially introduced basic solution of a material selected from the group consisting of sodium bicarbonate, sodiumtetraborate, disodium phosphate, and trisodium phosphate, and the overflow from said final wash bath; and third, in said final wash bath of deionized water.

5. The process improvement of claim 4 whereinsaid washing of said fibers is conducted in a continuously flowing trough, the flow direction being toward the point of entry into the trough of the fiber.

6. The process improvement of claim 4 wherein said washing of said fibers is conducted in each of three separate bathing containers, the overflow of the third of which flows into the second, and the overflow of the second of which flows into the first.

(References on following page) References Cited UNITED STATES PATENTS Cline 264-233X Rodgers 26438X Hooper 264-38 Severini 264-233UX Griset 264-233UX Sakurai et a1 264-38 Fujisaki et a1. 26478 8 3,121,765 2/1964 Kanda et a1. 264233X 3,318,983 5/1967 Hovis 264233X 3,124,631 3/1964 Davis 264233UX JULIUS FROME, Primary Examiner I. H. WOO, Assistant Examiner US. Cl. X.R. 

